This invention relates to intumescent, flame retardant polyurethane compositions containing an ammonium polyphosphate and a salt selected from melammonium pentate, pentate salt of ammelide, and mixtures of such salts, and optionally, triaryl phosphate. Such compositions are non-halogen, flame retardant, drip retardant during combustion, and are used at a level whereby the properties of the polyurethanes are not substantially degraded.
It is generally desirable to employ as little as possible of a flame retardant in the polyurethane compositions in order to minimize deleterious side effects on the physical properties. Examples of properties that are affected by the incorporation of flame retardants include elastic modulus, elongation at break, resilience, abrasion resistance, and thermal deformation temperature. Non-melting, particulate additives tend to be especially damaging to elastic properties whereas soluble, plasticizing additives tend to reduce thermal resistance.
Intumescent fire retardant compounds are characterized by their foaming and char-forming properties. The phenomenon of intumescent fire retardance is based on the production from the reagents of gaseous materials which expand the sample into a charred carbonaceous foam on heating. The charred foam is an insulator of low combustibility which, at the same time, retards the release of flammable gases from the heated mass.
Thermoplastic urethane elastomers, unlike most cross-linked rubbery materials, are readily processable by blow-molding, extrusion and injection molding equipment. Because of superior toughness and abrasion resistance, thermoplastic polyurethanes have found applications in such diverse uses as automotive fender extensions, roller skate wheels, pneumatic tubing, horseshoes, coated fabrics, wire and cable jackets, and the like.
Polyurethanes resins are, however, generally regarded as flammable, ranging from rapid-burning unmodified foam structures to slow-burning molded products. These materials also tend to degrade during burning to produce very low viscosity molten materials which tend to drip badly and spread the fire through flaming droplets.
Flame retarded polyurethane elastomer compositions containing halogen or phosphorus compounds are well known. Although such compositions are self-extinguishing and meet the UL-94 VO standard, the use of halogen-based flame retardants is not desirable for some applications. Halogen flame retardants, whether used alone or in conjunction with synergists such as antimony oxide, can limit the potential applications of the resin because they can produce undesirable acid vapors during decomposition. In the past, about 1 to 10%, on weight of the resin, of antimony compounds were added to the resin for flame-proofing. Antimony trioxide of fine particle size was used in preferred embodiments. Halogen compounds were also used in amount of 3 to 30%, based on the weight of the resin.
As already noted, thermoplastic polyurethane elastomers melt when exposed to flame and tend to contribute to spread of the fire by means of a flaming drip. Hence, drip retardation is a major consideration for any thermoplastic polyurethane flame retardant systems. Drip retardant, halogen-based thermoplastic polyurethane compositions exist, but they are objectionable in some applications due to vapor toxicity and corrosivity on combustion. Drip retardant, non-halogen or halogen-free based thermoplastic polyurethane compositions are also known but tend to require very high loadings which significantly reduce the key physical properties. This is particularly true of the softer thermoplastic polyurethanes which are desirable in the wire and cable industry for their superior flexibility at low temperatures.
Several patents appear to be pertinent to the subject matter claimed herein on the basis of disclosing a principal component thereof. U.S. Pat. No. 4,193,945 discloses self-extinguishing compositions comprising a polyolefin, an ammonium phosphate or polyphosphate, and a nitrogen-containing compound or a reaction product thereof with formaldehyde. The nitrogen-containing compounds are disclosed at bottom of column 1 but do not appear to be pertinent to the patentability issues herein. U.S. Pat. No. 4,201,705 discloses intumescent, non-dripping, flame retardant compositions containing a polyolefin and a flame retardant melammonium pentate or pentate salt of ammelide. A polyol can also be used in conjunction with the flame retardant. U.S. Pat. No. 4,253,972 discloses compositions comprising a polyolefin, an intumescent flame retardant melammonium pentate or pentate salt of ammelide, together with a polyhydric alcohol. U.S. Pat. No. 4,336,182 discloses anti-foaming and self-extinguishing compositions comprising a thermoplastic polymer such as polyolefin; a compound selected from amine phosphates, ammonium phosphates, and ammonium polyphosphates; together with a nitrogen-containing product. U.S. Pat. No. 4,342,682 discloses thermoplastic polyurethane elastomer compositions containing an intumescent additive melammonium pentate or pentate salt of ammelide together with a polyol. U.S. Pat. No. 4,363,906 discloses a solid water-insoluble condensation product of N,N'-ethyleneurea and formaldehyde that is different from a similar product disclosed in U.S. Pat. No. 4,193,945 and which is a better flame retardant for thermoplastic polymers, such as polypropylene, when combined with ammonium phosphate or polyphosphate. U.S. Pat. No. 4,404,291 discloses intumescent, fire retardant compositions for various polymers, including polyurethane resins, comprising a thermolized or heat-treated product obtained by reacting P.sub.2 O.sub.5 or a P.sub.2 O.sub.5 precursor with triethanolamine heated to expel volatiles.